In my prior patents, U.S. Pat. Nos. 3,906,547 and 3,055,013, I have disclosed helmet assemblies having visors movable between a lowered position in front of the wearer's face and a raised position behind a relatively rigid cover member. The visor may be releasable for movement by gravity to lowered position and may be locked in raised and lowered position. The visor may be movable to raised and lowered position and releasably held in those and intermediate position by detents and the like. While these helmet assemblies operate satisfactorily, it is desirable in certain military applications that the visor be rapidly and positively moved to its lowered position in response to the simple push of a finger, for example. Existing visor locks using screws or the like are relatively slow in operation and are difficult to operate with only one hand. Gravity does not provide the quick and certain action required.